upgraded to QtCreator 6 by mistake on Ubuntu 18.04, now there is no way back

I have an ancient build machine with Ubuntu 18.04, which is still the oldest LTS of Ubuntu and will remain as such till 2023. I ran QtMaintenance tool which offered updating my Qt components. So I upgraded to QtCreator 6.0 (from 5.0). Unfortunately, as I have found, QtCreator 6.0 does not run on Ubuntu 18.04 because it is built with Qt6 and therefore requires glibc 2.28, which is not available on Ubuntu 18.04.

I would like to downgrade to QtCreator 5.0 or any other version which does not require glibc 2.28. There seems to be no way of doing this. QtMaintenance tool does not offer older versions of QtCreator. Or is there any way?